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A leaf (pl.: leaves) is a principal appendage of the stem of a vascular plant, [1] usually borne laterally above ground and specialized for photosynthesis.Leaves are collectively called foliage, as in "autumn foliage", [2] [3] while the leaves, stem, flower, and fruit collectively form the shoot system. [4]
This layer contains mostly non-woody vegetation, or ground cover, growing in the forest with heights of up to about one and a half metres. The herb layer consists of various herbaceous plants ( therophytes , geophytes , cryptophytes , hemicryptophytes ), dwarf shrubs ( chamaephytes ) as well as young shrubs or tree seedlings .
The leaves are microphylls, each containing only a single vein and measuring less than 1 cm (0.4 inches) long. Two types of microphylls are formed, green trophophylls that cover most of the aerial shoots, and yellow to tan sporophylls that form the strobili, and contain the sporangia .
The root has depth zero, leaves have height zero, and a tree with only a single vertex (hence both a root and leaf) has depth and height zero. Conventionally, an empty tree (a tree with no vertices, if such are allowed) has depth and height −1. A k-ary tree (for nonnegative integers k) is a rooted tree in which each vertex has at most k children.
Prop-roots – In some dome-shaped (deliquescent) trees, from the mature horizontal boughs (stem-branches) some quite thick (millimeters to centimeters) roots come down. After growing and reaching the ground, they establish more elaborate root branches as well as show massive secondary thickening. Thus, they start to resemble the main trunk.
Banyan trees are an example of a strangler fig that begins life as an epiphyte in the crown of another tree. Their roots grow down and around the stem of the host, their growth accelerating once the ground has been reached. Over time, the roots coalesce to form a pseudotrunk, which may give the appearance that it is strangling the host.
Adventitious roots arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in monocots and pteridophytes, but also in many dicots , such as clover ( Trifolium ), ivy ( Hedera ), strawberry ( Fragaria ) and willow ( Salix ).
Fibrous roots grow fairly close to the surface of the ground. Leaves with parallel venation have fibrous roots. Forages have a fibrous root system, which helps combat erosion by anchoring the plants to the top layer of the soil, and covering the entirety of the field, as it is a non-row crop. [2]